The hemlock woolly adelgid (HWA) is an invasive, aphid-like insect. It was first reported in the U.S. in Virginia in 1951. In New England, the insect attacks and--over a period of years--kills eastern hemlock trees. Millions of trees have been infested or killed from Georgia to southeastern Maine.

Ecologist Dave Orwig oversees HWA research at the Harvard Forest and across southern New England.